Meningiomas are the most common extra-axial neoplasms in the
central nervous system. Their histological classification in 3 grades according
to the World Health Organization: benign (I), atypical (II), and
malignant (III), wich predicts the biological behavior and progressionfree
survival. The image study of choice is magnetic resonance.

OBJECTIVE: measure and determine the mean values of the apparent
diffusion coefficient in atypical and malignant meningiomas, and
evaluate its usefulness in preoperative distinction of those subtypes.

MATERIALS AND METHODS: we conducted a retrospective, observational
study at Instituto Nacional de Neurología y Neurocirugía Manuel
Velasco Suarez de Mexico (INNN), from January 2011 to July 2015,
including patients with diagnosis of grade II or III meningiomas in the
pathology archive who also had magnetic resonance and diffusion
studies in the picture archiving and communication system (PACS).

RESULTS: we identified 84 patients, 67 with histological diagnosis
of atypical meningiomas and 17 with malignant meningiomas. The
mean value of the apparent diffusion coefficient measured in patients
with grade II meningiomas was 0.820 × 10-3 mm²/s (± 0.150) and in
those with grade III meningiomas it was 0.770 × 10-3 mm²/s (± 0.125).

CONCLUSIONS: there were no statistically significant differences
between apparent diffusion coefficient values for atypical and malignant
subtypes (p = 0.336), although comparing them with the
literature available, our mean values are similar to those reported
by other authors and lower than those found in those obtained from
benign meningiomas.